1. Field of the Invention
This invention relates to a method of and a fluid additive for treating subterranean formations containing clays. The additive finds particular use in aqueous stimulation fluids such as fracturing fluids.
2. Prior Art
The production of oil and gas from subterranean formations which contain clays and other fines is often impeded by the unstable nature of these materials. Clays and fines when in an undisturbed condition are stable and cause no obstruction to the flow of hydrocarbons through the formation. However, when these materials are disturbed by contact with an aqueous fluid that is foreign to the formation, the clays can swell and the fines can migrate through the capillary flow channels in the formation resulting in a reduction of formation permeability, which is sometimes referred to herein as formation damage.
Attempts to diminish the damaging effects of introduced aqueous fluids upon subterranean formations have included the conversion of clay contained in the formations from a swelling form to a less swelling form. This method of control has featured the addition of various salts to the aqueous fluids utilized in the treatment of subterranean formations. Inorganic salts such as potassium chloride, calcium chloride, and ammonium chloride have been dissolved in an aqueous fluid utilized to treat a formation. The solubilized salts enter into a cation exchange with the charged particles comprising the clays. While these salts often do diminish the reduction of formation permeability, they can be detrimental to the performance of other constituents of the treatment fluid. For example, the salts which are typically admixed with the aqueous fluid before admixture of any viscosifying or gelling agents to the aqueous fluid, may have a detrimental effect upon the viscosity yield by the gelling agent upon hydration in the aqueous fluid.
Furthermore, such salts, and particularly those containing chloride ions, are finding environmental objections and are therefore preferably to be avoided. Accordingly, it would be desirable to provide an environmentally acceptable method and additive by which a subterranean formation can be protected from the damaging effects of foreign aqueous fluids wherein the treating fluid used can be prepared simply and without detrimental effects to fluid constituents.